Extrapolation of stress rupture data on 9 to 12% Cr steels

European Commission Directorate-General For The Information Society And Media Directorate-General For Research And Innovation

Description

Nuclear energy and safety
Energy research

Informations

• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 29
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Commission of the European Communities
nuclear science
and technology
Extrapolation of stress rupture
data on 9 to 12% Cr steels
Report
EUR 12388 EN Commission of the European Communities
nuclear science
and technology
Extrapolation of stress rupture
data on 9 to 12% Cr steels
D.S. Wood UKAEA, Risley, UK
C. Escaravage Novatome, Lyon, F
W. Ohly Interatom, Bergisch Gladbach, D
K. Williamson, Risley, UK
UKAEA
Risley Nuclear Power Development
Establishment Risley
Warrington, Cheshire WA3 6AT
United Kingdom
Contract No RA1-0106-UK
Final report
This work was performed under the
Commission of the European Communities
for the: Working group Codes and Standards
Activity Group 3 'Materials'
within the Fast reactor Coordinating Committee
Directorate-General Science,
Research and Development
1989 EUR 12388 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L-2920 Luxembourg
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of then is responsible for the use which might be made of
the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1989
ISBN 92-826-0818-2 Catalogue number: CD-NA-12388-EN-C
© ECSC-EEC-EAEC, Brussels · Luxembourg, 1989
Printed in Belgium Foreword and Executive Summary
The Commission of the European Communities is assisted in its
actions regarding fast breeder reactors by the Fast Reactor Coor­
dinating Committee which has set up the Safety Working Group and
the Working Group Codes and Standards (WGCS). The latter's man­
date is to harmonize the codes, standards and regulations used in
the EC member countries for the design, material selection, cons­
truction and inspection of LMFBR Components.
The present report is the revised final report of CEC Study Con­
tract N° RA1-0106-UK performed under WGCS/Activity Group 3 :
Materials. As most AG3 work, this study concerned the evaluation
of material data to be used in LMFBR design codes. The main
contractor was UKAEA with Novatome (France) and Interatom (FRG) as
participants.
This report addresses the problem of the extrapolation of stress
rupture data of 9-12% Cr steels to long times up to 300,000h.
These steels are used in steam generators of fossil fired and
nuclear plant operating at high temperatures where good creep
resistance and corrosion resistance are necessary. One of the
most important properties is that relating to the stress rupture
behaviour, in particular the long term stress rupture strength and
ductility.
The steels examined are : 9CrlMo extensively used in the UK,
9Cr2MoNbV extensively used in France and other European countries,
9CrlMoVNb (commonly designated Grade 91) recently developed in the
USA and of considerable interest to the European nuclear industry,
and two grades of 12CrMoV on which considerable experience has
been gained in Germany. The data on these steels comprised some
1500 data points coming from 222 casts and covered temperatures
ranging from 425°C to 650°C and durations from 1 to 100,000h (only
4 data points on one steel above 100,000h).
Four parameters were used for fitting the stress rupture strength
data: Larson-Miller, Orr-Sherby-Dorn (original), Orr-Sherby-Dorn
(ORNL) and Manson-Haferd. The predictions given by these four
parameters for 500°C and 300,000h fell within the following
ranges :
9CrlMo 135 | 6 MPa
9Cr2MoNbV 237 ± 5a
9CrlMoVNb 225 | 3 MPa
12CrMoV 154 - 9a
Thus the predicted long term average stress rupture strength was
little affected by the parameter employed at 500°C, relevant to
LMFBK steam generators. For each steel the predicted 10,000h and 100,000h average strength
values were compared throughout the whole investigated temperature
range with those given in the specifications. The predicted
values were close to those specified in ISO and RCC-MR for the
three 9% Cr steels. For the 12% Cr steel, however, thed
strength was considerably below the values specified in VDEH and
this difference requires further investigation.
The lower 95% confidence limits for stress rupture strength were
compared with average values. At 100,000h the ratio S (95%) / S
(ave) varied from 0.68 to 0.91 ; this contrasts with the usually
assumed minimum set at 80% of the average.
Stress rupture ductility was also analysed statistically. The
9Cr2MoNbV and the 12CrMoV steels exhibited a significant reduction
in ductility with increasing rupture time, whereas the two other
steels gave ductility values which were relatively independent of
rupture time.
L.H. Larsson
CEC/DGXII-D1
IV CONTENTS PAGE
1 1. INTRODUCTION
1 2. STEELS EXAMINED
2 3. EXTENT OF DATA
4. PARAMETERS USED FOR STRENGTH CALCULATIONS 2
Larson-Miller 3 ,
Orr-Sherby-Dorn (ORNL) 3 n (original) 4
Manson-Haferd
5. RESULTS OF CREEP RUPTURE STRENGTH ANALYSIS 5
5.1 Average Strength
5.1 .1 . 9CrlMo steel
5.1.2. 9Cr2MoNbV steel 6
5.1.3. 9CrlMoVNb steel
5.1.4. 12CrMoV steel 7
5.2 Comparison With Specified Strength Values 7
5.3n of the Strengths of the Steels 8
5.4 Minimum Stress Rupture Strength 9
6. STATISTICAL APPROACH TO STRESS RUPTURE DUCTILITY 10
6.1 General 1
6.2 9CrlMo, 9Cr2MoNbV and 9CrlMoVNb Steels 1
6.3 12CrMoV Steel1
7. RESULTS OF STRESS RUPTURE DUCTILITY ANALYSIS
7.1 9CrlMo Steel 1
7.2 9Cr2MoNbV Steel2
7.3 9CrlMoVNb Steel
7.4 12CrMoV Steel
8. CONCLUSIONS3
TABLES 1-10 15-35
FIGURES 1-72 36-107
- V -1. INTRODUCTION
9-12% Cr steels are used in steam generators of fossil fired and nuclear
plant operating at high temperatures where good creep resistance and corrosion
resistance are necessary. Various steels are available for such use, the
choice depending on a number of factors in addition to those already mentioned
such as ease of fabrication weldability and service experience. To assist in -
the selection it is necessary to compare the properties of the steels of
interest. One of the most important properties is that relating to the stress
rupture behaviour, and in particular the long term stress rupture strength for
example at 300,000h. In an earlier CEC Study Contract (RAP 092) relevant data
were collected. This document details the extrapolation of the stress rupture
strength data and the statistical evaluation of the stress rupture ductility.
2. STEELS EXAMINED
The steels examined comprise 9CrlMo (UKAEA), 9Cr2MoNbV (Novatome),
9CrlMoVNb (Novatome) and two grades of 12CrMoV (Interatom).
The specifications chemical compositions, heat treatments and tensile
properties are given in Tables 1 and 2.
9CrlMo steel is used extensively in the UK; it can be used in the
normalised and tempered or annealed condition. The N+T condition is generally
preferred however, and only this heat treatment condition has been considered
in this document.
9Cr2MoNbV steel is used extensively in France and other European
countries; it is commonly referred to as EM12. Unlike the other steels
considered it has a duplex microstructure containing ferrite.
ï
9CrlMoVNb steel, commonly designated Grade 91, is a steel which has
recently been developed in the USA and is of considerable interest within the
European nuclear industry. Having only recently been developed, the service
experience with this steel is very limited. In the case of the 12CrMoV steel, two specifications are covered, one of
medium tensile strength, 1.4922, and one of high tensile strength, 1.4923.
Similar steels containing tungsten were included in the data bank since it has
been shown that tungsten does not affect the stress rupture strength.
Considerable experience has been gained in Germany with 12CrMoV steels.
3. EXTENT OF DATA
The extent of the data broken down into different time intervals is shown
in Table 3.
Data on 9CrlMo steel cover 80 casts, a temperature range of 425-650°C,
and 789 data points with some exceeding 100,000h duration. For 9Cr2MoNbV steel
296 data points are available from 20 casts and cover the temperature range
550-650°C; a few points exceed 30,000h duration. In the case of 9CrlMoVNb
steel 220 data points are available from 36 casts but very few data points
exceed durations of 20,000h. Regarding the 12CrMoV steels 538 data points
are available from 40 casts for steel 1.4922 and 885 data points from 46 casts
for steel 1.4923; the data cover the temperature range 500-650°C and for both
steels a number of data points exceed 60,000h duration.
In the case of the 12CrMoV steel Interatom found that the data were too
extensive to be handled satisfactorily by the computer available to them. The
data on the 1.4922 steel were supplied by VDEH and Sandvik; the extrapolation
exercise was performed only on those data points provided by VDEH (156
points).
4. PARAMETERS USED FOR STRENGTH CALCULATIONS
The stress rupture strength data were treated